Subarachnoid haemorrhage

Subarachnoid haemorrhage is bleeding into the space between the subarachnoid membrane and the pia mater.

It accounts for 5-10% of all strokes.
Incidence is 8-10 cases per 100 000 per year.
It is most frequent in those aged 55 to 60.
SAH accounts for 3% of patients presenting to ED with headache.

Classical presentation is a thunderclap occipital headache - "as if kicked in head"-  with vomiting and neck stiffness.
Sentinel headache is now seen as less relevant.

Causes of SAH:
  • ruptured berry aneurysm (75%)
  • malformations (5%)
  • idiopathic
  • (post trauma)

Common sites of berry aneurysms are:
  • junction of the posterior communicating artery with the internal carotid
  • junction of the anterior communicating artery with the anterior cerebral artery
  • the bifurcation of the middle cerebral artery

20% of berry aneurysms are multiple.
Subarachnoid haemorrhages are associated with:

Investigation is:
  • CT - >90% of bleeds detected within 24 hrs; sensitivity declines rapidly after 10 days
  • LP - done >12hrs after onset looking for xanthochromia. If the analysis of fluid will be delayed the sample should be protected from light to prevent degradation of bilirubin

  • neurosurgical referral – coiling is now replacing clipping as the treatment of choice
  • prompt angiography if surgery likely
  • nimodipine
  • possibly hyperventilation – cerebral vasculature reacts to arterial CO2 tension so lower CO2 would lower ICP

  • 30 day mortality rate of 45%
  • Predictors of mortality are age, decreased GCS on admission and large volume of blood on initial CT
  • a third of survivors moderately to severely disabled
  • most re-bleeds occur in the first 3 weeks

  • rebleeding
  • hydrocephalus – 20%
  • cardiac dysfunction
  • hyponatraemia – 30%
  • hypomagnesaemia – associated with poor outcome; consider replacement if <0.7mmol

Small print gem: ECG abnormalities are common and troponin is raised in up to 30% of cases. It is thought this is because of excessive myocardial catecholamine release, caused by the SAH.

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